Method for cutting the edges of a continuous glass ribbon, a device for implementing said method, and a glass plate cut using said method

ABSTRACT

A method for cutting the edges of a continuous glass ribbon ( 10 ), moving at a speed VR, comprising a longitudinal marking stage which generates a marking line, in particular using a cutting wheel ( 11 ), a transverse marking stage, and a subsequent transverse breaking stage. The inventive method also comprises an intermediary stage between the longitudinal marking stage and the transverse marking stage consisting in generating at least one longitudinal fissure ( 32 ) through at least a substantial part of the thickness of the continuous glass ribbon, or through the entire thickness of the continuous glass ribbon, on the basis of the marking line ( 30 ), and in spreading said longitudinal fissure at a speed VF, which is more or less equal to but in the opposite direction to the speed VR of the moving continuous glass ribbon. The invention also relates to a device designed to carry out said method. The glass plates cut using the inventive method have edges, advantageously, without any major defects.

[0001] The invention relates to the field of the production of flatglass and relates more specifically to a method for cutting a continuousglass ribbon.

[0002] A continuous glass ribbon is to be understood as meaning a glassribbon coming from a continuous forming process, particular a floatprocess or a glass rolling process.

[0003] In general, a continuous glass ribbon is produced from aglassmaking furnace into which vitrifiable raw materials are introducedand melted to form a viscous glass. This viscous glass is fed to aforming tool, such as a float for example, where the viscous glass ispoured out onto a bath of molten tin held in a reducing atmosphere, or arolling mill. This then yields, at the output from the forming tool, acontinuous glass ribbon that has to be cut for later applications,particularly for applications in the field of building and/or the motorvehicle.

[0004] The traditional method used for cutting glass consists first ofall in annealing the glass ribbon then in cutting it in the transversedirection into plates and then cutting the edges off these plates in thelongitudinal direction.

[0005] The term “annealing” is given, in the usual way, to the operationthat consists in causing the glass ribbon to undergo a controlledcooling cycle so as to progressively relieve the stresses induced by theforming step.

[0006] The “transverse direction” is the term given to an axis roughlyperpendicular to the axis of travel of the glass ribbon leaving theforming tool.

[0007] The term “longitudinal direction” is given to an axis roughlyparallel to the axis of travel of the glass ribbon leaving the formingtool.

[0008] The term “plates” is given to elements of the glass ribbon onceit has been cut in the transverse direction.

[0009] The traditional method of cutting a continuous glass ribboninvolves four main steps after the glass ribbon has been annealed:

[0010] first step: longitudinal marking, particularly using a cuttingwheel, of a roughly continuous notch along each of the edges of one sideof the ribbon in the longitudinal direction. This marking is performed afew centimeters to a few tens of centimeters away from the outside edgeof the ribbon. Its purpose is to create surface defects on the glass toprepare for the subsequent cutting-off of the edges of the ribbon, anoperation known as “edge trimming”.

[0011] second step: marking a continuous notch along one side of theribbon in the transverse direction. This marking is performed inparticular with a cutting wheel which moves at an angle to the axis oftravel of the glass ribbon, so as to obtain on the ribbon a markingperpendicular to the axis of travel.

[0012] third step: division of the ribbon at the transverse marking toform a plate from the continuous ribbon. This step is known as“transverse breakage”. The plate thus formed is then generallytransported by rolls at a rate very much higher than the velocity atwhich the continuous ribbon travels.

[0013] fourth step “edge trimming”: separation of the region between theoutside edge of the plate and the marked line, the region termed the“edge”, from the remainder of the plate to obtain a plate whichconstitutes a finished or part-finished product which is then stored,generally roughly vertically, then dispatched to the customer on easels.

[0014] This fourth step, the edge trimming, first of all comprises aphase in which a shock is produced, for example using a metal wheel, atthe top of the plate, at the location where the longitudinal marking wasmade. The shock creates an addition of energy such that a crack developsand follows the fault line of the marking. A crack generated under theseconditions propagates very quickly, particularly at the speed of sound,namely about 1 000 m per second. The edge strip becomes detachedtherefore from the plate and is removed. In the case of thick glass, thepropagation of the crack may be assisted with the use of hammers,particularly pneumatic ones, that generate regular impacts on theunderside of the plate.

[0015] The transverse-breakage technique is described in particular inpatent U.S. Pat. No. 4,072,259.

[0016] The edge trimming technique has been improved many times, thesebeing set out, for example, in patents U.S. Pat. No. 4,196,830, U.S.Pat. No. 4,285,451, U.S. Pat. No. 4,466,562 and U.S. Pat. No. 4,489,870.

[0017] Those patents describe improvements to the conventional techniquementioned hereinabove, particularly and respectively the possibility ofeasing the edge trimming by local heating/cooling of the glass, ofcutting off the edges from two parallel longitudinal markings on thesame side, or from two longitudinal markings facing each other, on eachside of the glass, of developing means to apply a moment to the edgestrip by applying a load close to the outside edge of the edge strip soas to open up the crack starting from the marking.

[0018] It will be noted that all these improvements relate to means thatcome into effect after the continuous ribbon has been cut to formplates, that is to say after the transverse breakage.

[0019] These traditional edge-trimming techniques are relatively wellsuited to the industrial processes used to produce glass of standardthickness, particularly between 3 and 8 mm thick.

[0020] However, numerous problems arise in cutting the edges off whenthe thickness of the ribbon is either smaller than or greater than thethickness used in standard glass.

[0021] In the case of thin glass, particularly where the thickness isless than or equal to 1 mm, splintering is very often observed (see, forexample: “lateral cracks”, Fractography of Glass—Bradt, R. C.; Tressler,R. E., Plenum Press, New York, 1994) on the trimmed edge face usingtraditional techniques. This type of defect detracts considerably fromthe mechanical properties of the glass. Such defects are unacceptable tothe customer and lead to very high reject rates.

[0022] In the case of thick glass, particularly where the thickness isgreater than or equal to 10 mm, particularly greater than or equal to 15mm, edge faces trimmed using the traditional techniques are found thathave numerous defects. On the one hand, the edge faces are not generallyperpendicular to the largest sides (the sides corresponding to thehorizontal faces of the continuous glass ribbon) but cut at a bevel.

[0023] Numerous defects that may cause mechanical weakness are alsofound, particularly those known by those skilled in the art as flakes,burrs, broken corners, and branched cracks.

[0024] This type of defect needs to be eliminated so that the plates canbe used as finished products, particularly in applications where it isdesirable to toughen the glass because the toughening operation veryhighly stresses defects in the glass and often leads to breakage ifdefects are present.

[0025] It should be noted that most production of thick glass isintended for applications where the glass needs to be toughened.

[0026] To eliminate such defects introduced by the edge trimming usingtraditional techniques, a shaping step is performed, this consisting inremoving material, particularly by abrasion, so as to straighten up theedges and obtain a face free of defects likely to lead to breakageduring toughening. This operation is lengthy and expensive.

[0027] The objective of the present invention is to overcome the abovedisadvantages, particularly by making it possible to obtain edge faceswhich, after edge trimming, are devoid of major defects and thus allowthe use of the plates produced with little or even no shaping, in thesubsequent steps that lead to the production of a finished orpart-finished product.

[0028] The problem of obtaining edge faces devoid of major defects afterthe edge trimming of plates originating from a continuous glass ribbonis solved by the use of a method for cutting the edges of a continuousglass ribbon traveling at a velocity VR, comprising a longitudinalmarking step that generates a marked line, particularly with a cuttingwheel, a subsequent transverse marking step, and then a transversebreaking step, and which comprises an intermediate step between thelongitudinal marking step and the transverse marking step that consistsin generating at least one longitudinal crack in at least a substantialpart of the thickness of the continuous glass ribbon, particularlythroughout the thickness of said continuous glass ribbon, from themarked line and in causing said longitudinal crack to propagate at avelocity V_(F) roughly equal to and in the opposite direction from thevelocity V_(R) at which the continuous glass ribbon is traveling.

[0029] The inventors actually have been able to demonstrate that it ispossible in this way to obtain plates with edges roughly perpendicularto the sides of said plates and that these edges have an almost smoothsurface, known by the name of mirrored surface.

[0030] This appreciable effect is particularly surprising because it isknown to those skilled in the art that the edges obtained after edgetrimming using the conventional techniques are of mediocre quality andhave numerous defects, particularly in the case of thin glass plates andthick glass plates.

[0031] With the method according to the invention, it is found that theedges are smooth and free of major defects for all glass platethicknesses, particularly for thick glass and thin glass.

[0032] Implementation of this method leads to a device that isremarkably simple, but highly effective.

[0033] The means used to generate a longitudinal crack areadvantageously arranged near each outside edge of the continuous glassribbon so as to propagate a crack simultaneously along each edge of theribbon and subsequently cause the trimming off of each of the edgestrips at the same time.

[0034] A crack is thus seen to appear along a line through a substantialpart of the thickness of the glass, particularly at least half thethickness, or even a penetrating crack, upstream of the means forgenerating the crack and downstream of the longitudinal marking means.In the remainder of this text, this crack will be known as the“longitudinal crack”. This longitudinal crack, visible with the nakedeye with practically all glasses, seems to be practically stationary toan observer situated beside the line. This is because the resultantvelocity between the velocity at which the glass ribbon is travelingV_(R) and the rate of propagation of the crack V_(F) is practicallyzero. “Practically” should be understood as meaning a possible variationof the order of a factor of 2. This variation may give an observersituated beside the line the impression that the crack is traveling,while at the same time remaining situated between the means generatingit and the longitudinal cutting means.

[0035] The variations in the velocity at which the crack propagates may,in particular, be associated with the heterogeneities of the residualstresses in the glass, following the annealing operation.

[0036] The continuous glass ribbon thus consists of three regions oncethe longitudinal crack has been generated: two edge regions and acentral region. When the crack is a penetrating one, these regions seemto be contiguous and it can usually be said that they “remain stuck”together, even though there is nothing holding them together. Thetransverse marking operation is then performed right across these threeregions. A breaking step follows on from this, in which step known meansare used to initiate and propagate a penetrating crack that leads to theparting of a plate from the glass ribbon.

[0037] Breaking is performed in particular by raising the ribbon at thetransverse marking level using a roll in contact with the ribbon acrossits entire width, placing its entire cross section into bending.

[0038] In the case of the method as claimed in the invention, this stephas a dual purpose because it gives rise both to the parting of theplate from the ribbon and also to the separation of the edge regions,the edge strips, which then detach themselves from the central regionand are collected in bins.

[0039] According to one embodiment of the invention, the longitudinalcrack is generated and propagates by progressive bending of thecontinuous glass ribbon in a region situated under the longitudinalmarked line between the longitudinal marking and the transverse marking.

[0040] In this way, the introduction of bending allows a longitudinalcrack to develop from the longitudinal marked line and it propagates inthe opposite direction to the direction in which the glass ribbon istraveling.

[0041] What happens is that the gradual bending allows very precisecontrol over the opening up of the longitudinal crack and control overthe rate at which the crack thus generated is propagated.

[0042] According to a particularly advantageous alternative form, thecontinuous glass ribbon is bent by applying a force F_(I) to theunderside of said continuous glass ribbon so as to lift the glass ribbonslightly in a region situated under the longitudinal marked line oralternatively near the longitudinal marked line on the side of this linefurthest away from the outside edge of the ribbon when considering theclosest outside edge.

[0043] To give a more concrete idea, the load applied to such a wheel isof the order of 1 000 N, that is to say preferably between 500 and 2 000N.

[0044] For a glass ribbon 15 mm thick from which it is desired to removeedges about 200 mm wide, it is possible in particular to apply a forceof about 900 N, when this force is applied about 70 cm from the fulcrum.

[0045] For a glass ribbon 19 mm thick, from which it is desired toremove edges about 250 mm wide, a force of about 1 200 N may inparticular be applied.

[0046] These indications are not in any way limiting because the loadthat has to be applied depends on the state of annealing of the glass,and the person skilled in the art can readily determine this by varyingsaid load may slightly observing the effect that this variation in loadhas on the progress of the longitudinal crack.

[0047] According to another preferred embodiment of the invention, aforce F_(s) is applied to the top side of the continuous glass ribbon ina region lying between the longitudinal marked line and the outside edgeof the continuous glass ribbon to contribute to the generation andpropagation of the longitudinal crack.

[0048] This embodiment is particularly suited to the production of glassof thin and medium thickness, and encourages the guidance of thelongitudinal crack so as to make it easier to cause it to propagate inline with the longitudinal marking.

[0049] Although the application of a bearing force to the top face isnot essential for thick glass, particularly glass more than 15 mm thick,this embodiment is not precluded with these glasses. It may even proveparticularly advantageous where there is a desire to reduce the width ofthe edge trimmings and thus make savings on material allowing theefficiency of the line to be increased.

[0050] According to another embodiment of the method according to theinvention, one or more applications of heat and/or of coolingcontributes or contribute to the generation and propagation of thelongitudinal crack.

[0051] The application of heat may, in particular, be obtained by use ofa laser beam which interacts with the glass, the laser beam beingcollimated to be focused onto the top side of the glass ribbon.

[0052] Cooling can be obtained in particular by at least one roll,preferably a roll situated on each side of the crack, in contact withthe underside of the glass. This type of cooling roll is likely to becooled by a liquid with which it is in contact, for example a cooledliquid contained in a tank into which the roll is plunged.

[0053] The invention also relates to a device designed to implement themethod according to the invention.

[0054] This device for cutting off the edges of a continuous glassribbon comprises longitudinal marking means, transverse marking means,transverse breaking means and further comprises means, particularlymechanical means, for generating and propagating the longitudinal crack.

[0055] In a preferred embodiment of the device according to theinvention, at least one mechanical means for generating and propagatingthe longitudinal crack is a wheel that can be brought into contact withthe underside of a continuous glass ribbon.

[0056] In a particularly advantageous version, at least one wheel isslaved by slaving means, particularly comprising a ram, particularlyconnected to a base, in such a way that either the position of thiswheel is fixed or the force F_(I) applied under the continuous glassribbon is constant.

[0057] According to one embodiment of this device, at least onemechanical means for generating and propagating the longitudinal crackis a wheel situated on the top side of the continuous glass ribbon, andparticularly connected to a ram.

[0058] It is possible, as an equivalent to the wheels described above,to use one or more rollers over which the glass can slide without beingdamaged. It is, for example, possible to use rollers made of coppercoated with a layer of MOS₂.

[0059] According to another alternative form of this device, themechanical means are replaced or supplemented by at least one means ofapplying heat or cooling to at least one region of one side of thecontinuous glass ribbon, this means being situated between thelongitudinal marking means and the transverse marking means.

[0060] According to a preferred embodiment, at least one means ofapplying heat and/or cooling is a heated (or cooled) roll in contactwith a top (or bottom) surface of the continuous glass ribbon.

[0061] In an equivalent way, it is possible to use a heated and/orcooled roller. Furthermore, a wheel and/or a roller may simultaneouslybe a mechanical means capable of applying a shape F_(I) or F_(s) underor on the glass ribbon, and be a means of respectively applying coolingor heating.

[0062] It is possible, for example, to use wheels or rollers throughwhich a heat transfer fluid, for example liquid nitrogen, or a heatedliquid, passes.

[0063] It is thus possible, by creating a thermal gradient in thethickness of the glass, to establish a stress system equivalent to thatestablished by bending and thus contribute to generating and propagatinga longitudinal crack.

[0064] According to another embodiment, at least one means of applyingheat is a laser.

[0065] The invention also relates to a glass plate obtained by themethod as claimed in the invention, where the longitudinal edge facesare more or less perpendicular to the underside and top side of theplate and has a mirrored surface.

[0066] As mentioned above, such a plate is particularly advantageousbecause it makes it possible to considerably reduce the subsequentshaping operations.

[0067] The thick glass plates according to the invention areparticularly well suited for producing products made of thick glass,particularly at least 10 mm thick, or 15 mm or more thick, and even 17mm or more thick, for example for applications in building or interiordecorating.

[0068] Thin glass plates according to the invention are particularlysuited for producing products in thin glass, particularly 1 mm thick orless, for example for applications as screens.

[0069] In general, the glass plates according to the invention areparticularly suited to the production of articles made of toughenedglass.

[0070] Other details and advantageous features of the invention willbecome apparent hereinbelow, from the description of some exemplaryembodiments of the invention with reference to the attached figureswhich depict:

[0071]FIG. 1: a part view from above of a line for producing and cuttinga continuous flat glass ribbon;

[0072]FIG. 2: a part view on section A-A′ of FIG. 1;

[0073]FIG. 3: a part view in section at right angles to the axis oftravel of the glass ribbon;

[0074]FIG. 4: an alternative form of the part view in section at rightangles to the axis of travel of the glass ribbon;

[0075]FIG. 5: a view of an edge-trimmed edge of a thick glass plateobtained from a continuous glass ribbon according to the conventionaledge-trimming techniques;

[0076]FIG. 6: a view of an edge-trimmed edge of a thick glass plateobtained from a continuous glass ribbon, according to the invention.

[0077] It is first of all emphasized that, for clarity, the variouselements depicted in the figures are not all strictly to scale.

[0078]FIG. 1 depicts a partial view from above of a line for producingand cutting a continuous flat glass ribbon.

[0079] The flat glass ribbon 10 usually comes from an annealing regionand enters the cutting region at a ribbon travel velocity denoted V_(R),carried by drive rolls 12. This ribbon generally has imperfections oneach of its external edges, these imperfections being due in particularto marking by tools, for example known as top rolls, to control thewidth of the ribbon by pulling or compressing the edges. In the case ofthick glass ribbon, the edges are generally not as thick as the averagethickness of the ribbon and, conversely, in the case of thin glassribbons, the edges are thicker than the average thickness of the ribbon.

[0080] To remove these edges, an edge trimming operation is performed.This operation usually begins with a longitudinal marking step, using amarking means 51 near each of the outside edges of the ribbon,particularly using a cutting wheel 11. A practically continuous notchedline 30 is thus marked into the glass in the longitudinal direction ofthe ribbon.

[0081] The line for producing and cutting the glass ribbon comprises,downstream of the longitudinal marking means 51, transverse markingmeans 52 that generate a transverse marked line 41, then a breakingmember here depicted in the form of a roll 53, which lifts up under eachtransverse marked line 41 to divide a plate 62 from the continuousribbon 10. The drive rolls 13, situated after the breaking member 53,drive the cut plates at a velocity V_(P) higher than the velocity atwhich the continuous ribbon V_(R) travels, so as to allow subsequentextraction of the plates, usually by lifting them up, after which theycan be stacked.

[0082] The invention provides a means located between the longitudinalmarking means 51 and the transverse marking means 52, for generating apenetrating crack from the longitudinal marked line 30. Here, this meanshas been depicted in the form of a wheel 21 situated under the glassribbon and mounted on a base bearing a ram 22.

[0083] This wheel is situated approximately mid-way between thelongitudinal marking means 51 and the transverse marking means 52. Thiswheel may in particular be situated a distance of 0.60 to 1 meterdownstream of the longitudinal marking means 51. A longitudinal crack,particularly a penetrating one, develops on each side of the outsideedges of the glass ribbon 10. After the transverse breaking operationobtained by virtue of the roll 53, the plate 61 separates from theribbon 10 and at the same time the edge strips 61 on each of the sideedges of the plate 62 separate and are removed.

[0084]FIG. 2 depicts a part view in section on A-A′ of the precedingfigure. The observation point is facing the edge face of the continuousglass ribbon 10 and makes it possible to provide further detail on thestep of generating and propagating the longitudinal crack 32. In thescenario depicted here, this longitudinal crack is a penetrating one.After the cutting wheel 11 has made its mark 30 on the top side 15 ofthe glass ribbon, the crack begins to develop from a point 31 known asthe top of the crack until it progressively passes through the thicknessof the edge face of the glass ribbon 10. This crack propagates at avelocity V_(F) in the opposite direction to the velocity at which theribbon V_(R) propagates, and of approximately equal magnitude.

[0085] In order to generate and propagate this crack 32, a force isapplied to the underside 17 of the glass ribbon using the wheel 21mounted on the ram 22 which is fixed to the ground by a support, forexample by the tripod 23.

[0086]FIG. 3 depicts a part view in section perpendicular to the axis oftravel of the glass ribbon, situated between the marking means 51 andthe wheel 21. This figure depicts an enlargement of the region close toan outside edge of the ribbon 10, in a view transverse to the axis oftravel of the ribbon. This provides further specifics as to the locationof the wheel 21 in contact with the underside 17 of the glass ribbon. Inthis depiction, the wheel 21 is situated in a region close to the crack32, situated on the opposite side of the marked line 30 from the outsideedge 16 of the glass ribbon 10. This wheel 21 may also be arranged underthe marked line 30. A force F_(I) is thus applied and this creates, inthe edge face of the ribbon, a region 35 that is in extension.

[0087] As shown also in FIG. 3, it is possible to use a wheel 25 bearingagainst the top side 15 of the glass ribbon and that allows a forceF_(s) to be applied, this force also contributing to generatingextensile stresses in line with the marked line 30, in the region 35.This wheel 25 is situated in the region lying between the marked line 30and the outside edge 16 of the glass ribbon 10.

[0088]FIG. 4 depicts an alternative form of the embodiment according tothe invention, observed from the same viewpoint as FIG. 3.

[0089] In this alternative form, rolls 81, 82 are arranged in contactwith the underside 17 of the continuous glass ribbon 10, on each side ofthe longitudinal marked line 30. These rolls are cooled by immersion ina liquid 85, at a temperature below ambient temperature, contained in abath 86.

[0090] This results in forces that lead to the generation followed bythe propagation of the crack 32 from the marked line 30.

[0091] Another embodiment of this alternative form may be obtained withrolls 81, 82 cooled by the circulation of liquid nitrogen within theserolls.

[0092] This device is particularly suited to the production of thinglass.

[0093] It is also possible to associate one of the above cooling systemswith the roll 21 described in FIG. 3.

[0094]FIG. 5 depicts the edge face 101 of a thick glass plate, the edgeof which has been trimmed off using traditional techniques. Thisobservation example corresponds to an edge face where the edge has beenparted by impact, particularly the shock of a pneumatic hammer tappingon the underside of the sheet to cause the crack to propagate to allowthe edge strips to be parted from the edges of the main body of theplate. Numerous defects can be seen, particularly lines 102 that lead tothe formation of flakes 103, a rough region 104 that can be attributedto the rapid propagation of the crack, and a region 105 generally at anangle.

[0095]FIG. 6 depicts the edge face 201 of a thick glass plate, the edgeof which has been trimmed off using the method according to theinvention. The surface of this edge face 201 is smooth. Note thepresence of the route of the longitudinal marked line 30. The regionsituated beyond this marked line is a mirror region 202.

[0096] The invention is not restricted to these particular embodimentsand must be interpreted nonlimitingly and as encompassing any method forcutting the edges of a continuous glass ribbon traveling at a velocityV_(R), comprising a longitudinal marking step that generates a markedline, particularly using a cutting wheel, a subsequent transversemarking step, followed by a transverse-breaking step and that comprisesan intermediate step between the longitudinal marking step and thetransverse marking step that consists in generating at least onelongitudinal crack in at least a substantial part of the thickness ofthe continuous glass ribbon, particularly throughout the thickness ofsaid continuous glass ribbon, from the marked line and in causing saidlongitudinal crack to propagate at a velocity V_(F) roughly equal to andin the opposite direction from the velocity V_(R) with which thecontinuous glass ribbon is traveling.

1. A method for cutting the edges of a continuous glass ribbon (10)traveling at a velocity (V_(R)), comprising a longitudinal marking step(at 51) that generates a marked line (30), particularly with a cuttingwheel (11), a subsequent transverse marking step (at 52), and then atransverse breaking step (at 53), characterized in that it comprises anintermediate step between the longitudinal marking step and thetransverse marking step that consists in generating at least onelongitudinal crack (32) in at least a substantial part of the thicknessof the continuous glass ribbon (10), particularly throughout thethickness of said continuous glass ribbon, from the marked line (30) andin causing said longitudinal crack (32) to propagate at a velocity(V_(F)) roughly equal to and in the opposite direction from the velocity(V_(R)) at which the continuous glass ribbon (10) is traveling.
 2. Thecutting method as claimed in claim 1, characterized in that thelongitudinal crack (32) is generated and propagates by progressivebending of the continuous glass ribbon (10) in a region (35) situatedunder the longitudinal marked line (30) between the longitudinal marking(at 51) and the transverse marking (at 52).
 3. The cutting method asclaimed in claim 2, characterized in that the continuous glass ribbon(10) is bent by applying a force (F_(I)) to the underside (17) of saidcontinuous glass ribbon (10) so as to lift the glass ribbon slightly ina region situated under the longitudinal marked line (30) oralternatively near the longitudinal marked line (30) on the side of thisline furthest away from the outside edge (16) of the ribbon (10) whenconsidering the closest outside edge.
 4. The cutting method as claimedin either one of claims 2 to 3, characterized in that a force (F_(s)) isapplied to the top side (15) of the continuous glass ribbon (10) in aregion lying between the longitudinal marked line (30) and the outsideedge (16) of the continuous glass ribbon (10) to contribute to thegeneration and propagation of the longitudinal crack (32).
 5. Thecutting method as claimed in any one of the preceding claims,characterized in that one or more additions of heat and/or of cooling(81, 82) contributes or contribute to the generation and propagation ofthe longitudinal crack (32).
 6. A device for implementing the method asclaimed in one of claims 1 to 5, characterized in that it compriseslongitudinal marking means (51), transverse marking means (52), breakingmeans (53) and means, particularly mechanical means (21, 22, 23, 25),for generating and propagating the longitudinal crack (32).
 7. Thedevice as claimed in claim 6, characterized in that at least onemechanical means for generating and propagating the longitudinal crack(32) is a wheel (21) that can be brought into contact with the underside(17) of a continuous glass ribbon (10).
 8. The device as claimed inclaim 7, characterized in that at least one wheel (21) is slaved byslaving means, particularly comprising a ram (22), particularlyconnected to a base (23), in such a way that either the position of thiswheel (21) is fixed or the force (F_(I)) applied under the continuousglass ribbon (10) is constant.
 9. The device as claimed in one of claims6 to 8, characterized in that at least one mechanical means forgenerating and propagating the longitudinal crack (32) is a wheel (25)situated on the top side (15) of the continuous glass ribbon (10), andparticularly connected to a ram.
 10. The device as claimed in one ofclaims 6 to 9, characterized in that it comprises at least one means ofapplying heat and/or cooling (81, 82) to at least one region of one sideof the continuous glass ribbon (10), this means being situated betweenthe longitudinal marking means (51) and the transverse marking means(52).
 11. The device as claimed in claim 10, characterized in that atleast one means of applying heat and/or cooling is a heated (or cooled)roll (81, 82) in contact with a top (15) (or bottom (17)) surface of thecontinuous glass ribbon (10).
 12. The device as claimed in one of claims10 and 11, characterized in that at least one means of applying heat isa laser.
 13. A glass plate (62) obtained by the method as claimed in oneof claims 1 to 5 or produced using the device as claimed in one ofclaims 6 to 12, characterized in that the longitudinal edge faces aremore or less perpendicular to the underside (17) and top side (15) ofthe plate and in that said longitudinal edge faces have a mirroredsurface (202).
 14. The use of the glass plate as claimed in claim 13 forproducing products made of thick glass, particularly at least 10 mmthick, or 15 mm or more thick, and even 17 mm or more thick, for examplefor applications in building or interior decorating.
 15. The use of theglass plate as claimed in claim 13 for producing products in thin glass,particularly 1 mm thick or less, for example for applications asscreens.
 16. The use of the glass plate as claimed in claim 13 forproducing articles made of toughened glass.